Point to point sub-interfaces are generally favored to allow for flexibility
in maintaining the configurations going forward. Split-horizon is not an
issue for OSPF, but may be an issue for other routing protocols that may
also share the physical interface at some point.

Split-horizon is not an issue for OSPF, but may be an issue for distance
vector (including EIGRP) routing protocols that may also share the physical
interface at some point.

Since there are just 2 sites connected to each other via NBMA frame-relay
and no requirement for one to be a multipoint hub, point to point
sub-interfaces are generally favored to allow for flexibility in maintaining
the configuration.